feat(branding): adaptive Android launcher icon

Split the logo into foreground/background layers so Android can
apply system masks (circle, squircle, teardrop) and parallax
instead of rendering a flat composited PNG.

- icons/logo_{foreground,background}.png: new canonical sources
- mipmap-*/ic_launcher_{foreground,background}.png: regenerated
  per density (108/162/216/324/432)
- mipmap-*/ic_launcher{,_round}.png: legacy pre-API-26 composites
- mipmap-anydpi-v26/ic_launcher.xml: background now points at
  @mipmap/ic_launcher_background instead of solid white @color
- mipmap-anydpi-v26/ic_launcher_round.xml: added so round
  launchers also get adaptive treatment
- drop unused @color/ic_launcher_background and the leftover
  Tauri-template drawable

Tauri app: 0.5.2 -> 0.5.3.

src-tauri/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "bocken"
-version = "0.5.2"
+version = "0.5.3"
 edition = "2021"
 
 [lib]